Radar system logic circuit

ABSTRACT

A dual frequency radar system that automatically switches from a resistive mixer of two receiving channels to a peak value selector. The switching is determined by the presence of signals in each channel above a given threshold.

[151 3,689,922 Phillips, Ill. Sept. 5, 1972 [54] RADAR SYSTEM LOGICCIRCUIT Primary Examiner-T. H. Tubbesing 72] Inventor; Calvert RPhillips, Jr Annapolis Attorney-Hany A. Herbert, Jr. and Julian L.Siege] [73] Assignee: The United States of America as [57] ABSTRACTPresented by the Secretary of-Air A dual frequency radar system thatautomatically Force switches from a resistive mixer of two receivingchan- [22] Filed: March 23, 1966 nels to a peak value selector. Theswitching is deter- I mined by the presence of signals in each channel[21] Appl' No" 538173 above a given threshold.

[52] US. Cl ..343/17.1 R, 343/18 E [51] Int. Cl ..G01s 7/28 [58] Fieldof Search ..343/17.l, 18 E [56] References Cited 3 Claims, 2 DrawingFigures UNITED STATES PATENTS 3,403,394 9/1968 Rouault ..343/l7.l R Xxx/44 news/wk R4041? 05,579.77

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JMPCY/ L q M w I RADAR SYSTEM LOGIC CIRCUIT This invention relates to adual frequency radar system and more particularly to a logic circuit forobtaining a high signal to noise ratio.

A radar system transmitting and receiving at two or more separate anddistinct frequencies has a number of inherent advantages in both ajamming and nonjamming environment. To fully utilize these inherentadvantages, it is necessary to employ receivers and logic circuits whichwill automatically provide optimum outputs. This invention presents twotechniques which may be employed to automatically provide optimumoutputs from a dual frequency radar system in either a jamming or anon-jamming environment with no manual selection required. The majorityof search radar systems used CFAR (Constant False Alarm Rate) receivers.CFAR receivers as the name applies provide a constant noise outputindependent of the type of jamming input, assuming proper receiverdesign. As a result, the logic circuits considered here are restrictedto use with CFAR receivers.

In a non-jamming environment, the target return will be present in bothreceiving channels of the dual frequency system the majority of thetime."Both receiving channels are assumed to have equal amplitudeuncorrelated noise, as would be expected. Under this con-' dition,linear resistive mixing produces optimum results in terms of maximumsignal to noise ratio. If, however, jamming occurs at one of the twotransmitting frequencies, the signal will be present in the unjammedchannel only. Under these conditions resistive mixing is no longerdesirable and the use of a peak selector, is desirable-from the viewpoint of producing an optimum signal to noise ratio in the outputsystem. It may be seen that a swept jammer sweeping between the tworadar frequencies would require a constant switching between theresistive mixer and the peak value selector unless an automatic logicselection circuit is employed.

It is therefore an object of this invention to provide a dual frequencyradar system having a optimum output;

It is another object to provide a dual frequency radar system usable ineither a jamming or non-jamming environment;

It is still another object to provide a dual frequency radar systemusing a logic circuit requiring no manual selection.

These and other advantages, features and objects of the invention willbecome more apparent from the following description taken in connectionwith the illustrative embodiments in the accompanying drawings, wherein:

FIG. 1 is a block diagram of one embodiment of the invention; and

FIG. 2 is a block diagram of a second embodiment of the invention.

Referring to FIG. 1, a logic circuit is shown employing AND gate 15 tofurnish the information required in either or both receiving channels 11and 12, there is no output from AND gate 15 and the output is taken frompeak value selector 18. As a result, optimum performance of the systemis automatically assured.

Referring to FIG. 2 another automatic selection 15 system is shown. Inthis system, the output of either peak value selector 25 or resistivemixer 14 is applied to another peak value selector 26 whichautomatically produces a maximum output for signals in either or both ofreceiving channels 11 and 12. Although the system shown in FIG. 2 isappreciably simpler than the system shown in FIG. 1, in terms of circuitcomplexity, the system of FIG. 2 produces a degradation in thenonjarnming signal to noise ratio. This degradation in signal to noiseratio is a result of the final peak selector 26 selecting the noisepeaks of either resistive mixer 24 or peak value selector 25, whichwould in turn increase the peak noise to signal ratio in the output. Ingeneral, however, the slight degradation of the signal to noise ratiowould be offset by the simplicity of the circuit of 30 FIG. 2 ascompared to FIG. 1.

I claim.

1. A dual frequency radar system employing a Constant False Alarm Ratecomprising:

a. a first and second receiver;

b. a resistive mixer fed by the first and second receivers;

c. a peak value selector fed by the first and second receivers;

d. an electronic switch connecting alternately the outputs of the peakvalue selector and the resistive mixer;

e. and an AND gate fed by the first and second receivers activating theelectronic switch.

2. A dual frequency radar system according to claim 1 which furtherincludes:

a. base line clippers interposed between the first and second receiversand the AND gate;

b. a first delay line interposed between the resistive mixer and theelectronic switch;

c. and a second delay line interposed between the peak value selectorand the electronic switch.

3. A dual frequency radar system employing a Constant False Alarm Ratecomprising:

a. a first and second receiver;

b. a resistive mixer fed by the first and second receivers;

c. a first peak value selector fed by the first and second receivers;

d. and a second peak value selector fed by the reto automaticallycontrol switch 21 for selecting either Sistive mixer and the first PValue Selectorpeak value selector 18 or resistive mixer 17. Delay lines

1. A dual frequency radar system employing a Constant False Alarm Ratecomprising: a. a first and second receiver; b. a resistive mixer fed bythe first and second receivers; c. a peak value selector fed by thefirst and second receivers; d. an electronic switch connectingalternately the outputs of the peak value selector and the resistivemixer; e. and an ''''AND'''' gate fed by the first and second receiversactivating the electronic switch.
 2. A dual frequency radar systemaccording to claim 1 which further includes: a. base line clippersinterposed between the first and second receivers and the ''''AND''''gate; b. a first delay line interposed between the resistive mixer andthe electronic switch; c. and a second delay line interposed between thepeak value selector and the electronic switch.
 3. A dual frequency radarsystem employing a Constant False Alarm Rate comprising: a. a first andsecond receiver; b. a resistive mixer fed by the first and secondreceivers; c. a first peak value selector fed by the first and secondreceivers; d. and a second peak value selector fed by the resistivemixer and the first peak value selector.